Former US Secretary of State Henry Kissinger warned Thursday that a "nuclear Iran" is "approaching" and urged relevant stakeholders to decide how to respond sooner rather than later.

"For 15 years, the permanent members of the Security Council have declared that a nuclear Iran is unacceptable, but it is approaching," the veteran former architect of US foreign policy told a meeting at the annual World Economic Forum (WEF).

"I believe this point will be reached in a very foreseeable future," he said at a plenary WEF meeting chaired by Klaus Schwab, founder and executive chairman of the WEF.

"So in a few years, people will have to come to a determination of how to react, or the consequences of non-reaction," he added.

While stressing that unilateral intervention by Israel would be "a desperate last resort," Kissinger warned against Iran using the negotiations as a tool to gain time to complete their nuclear program.

"The Iranians have to understand that if they keep using the negotiations to gain time to complete a nuclear program then the situation will become extremely dangerous," he said.

"The consequences of an Iranian nuclear program is that other countries in the area will also want nuclear weapons," and when nuclear weapons become "almost conventional," "we would face a nuclear war at some point, which would be a turning point in world history," he said.

Iran and the West are locked in a bitter dispute over the former's nuclear ambitions. The West accuses Tehran of developing nuclear weapon under the cover of peaceful nuclear program, a charge Iran has consistently denied.

On the Syria crisis, Kissinger said there was no easy solution.

The world would face "a huge human tragedy" if it stands on the sidelines and does not intervene, but "if it does intervene, it will be in middle of vast ethnic conflict."

However, the current conflict in Syria can be resolved if the United States and Russia were to sponsor an agreement that other countries would also back, he said.